Method for conveying container, device for conveying container, and method for conveying ladle

ABSTRACT

A method for calculating a conveyance velocity at which oscillation of a liquid surface is suppressed in conveying a container in which a liquid is accommodated, e.g., a ladle in which molten metal is accommodated. In a graph of conveyance velocity versus conveyance time, an upwardly convex parabola and a downwardly convex parabola having vertical symmetry are prepared in advance, the downwardly convex parabola and the upwardly convex parabola are smoothly connected to form an acceleration curve, the upwardly convex parabola and the downwardly convex parabola are smoothly connected to form a deceleration curve, and the conveyance velocity is obtained from the acceleration curve and the deceleration curve smoothly connected where the slope thereof is zero.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for conveying a containercontaining a liquid, and more particularly to a method for conveying aladle containing molten metal.

BACKGROUND OF THE INVENTION

An example of conveyance of a container containing a liquid is aconveyance of a ladle in a casting line. During this conveyance, afterthe ladle is conveyed to a pouring position, oscillations may begenerated on a surface of molten metal in the ladle. If suchoscillations continue for a long time, measurement of the ladle weightbecomes unstable, which may affect feeding accuracy of the molten metal.

It has been known that such oscillations of a liquid surface can besuppressed by making a curve of acceleration and deceleration in a graphof velocity versus time of ladle conveyance an S shape. It has been alsoknown that such an S-shaped curve can be calculated from a liquidsimulation (Patent Document 1 for example).

RELATED ART Patent Documents

-   [Patent Document 1] Japanese Unexamined Patent Application    Publication No. H9-10924 (JP-A-H9-10924)

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

As described in Patent Document 1, the calculation of the curve from aliquid simulation requires complex calculations using a plurality ofparameters, such as conditions of the ladle and the molten metal,conveyance distance, conveyance time, and so on. However, it is oftenrequired in a casting line to change a ladle for another or to changethe conveyance distance according to positions of molds. In such cases,it is required to change the above parameters according to theconditions and to do the complex calculations over again. That is,applying a liquid simulation to a conveyance of a ladle in a castingline may complicate setting of the conveyance velocity.

On the other hand, in a casting line, there is sometimes a case in whichoscillations of a liquid surface during a pouring operation afterconveying the ladle can be tolerated to an extent. That is, there is acase in which a pouring operation can be done while the liquid surfaceis not completely stationary. Thus, rather than to calculate the optimumconveyance velocity by using a liquid simulation, it is sometimespreferable to be able to more easily calculate the conveyance velocityat which the liquid surface oscillations are suppressed to an extent.

An object of the present invention is to provide a method for conveyinga container and a method for conveying a ladle, which facilitatescalculation of a conveyance velocity at which liquid surfaceoscillations are suppressed in conveying the container containing aliquid, or the ladle containing molten metal.

Means for Solving Problems

A first invention is a method for conveying a container. The methodstarts a conveyance by accelerating the container containing a liquid ina horizontal direction and decelerates the container to complete theconveyance. A conveyance velocity v(t) of the container, which is afunction of time t, can be represented by:

Formula 1 when 0≤t≤(t₀/4)

v(t)=a·t ²  [Formula 1]

Formula 2 when (t₀/4)≤t≤(3t₀/4)

$\begin{matrix}{{v(t)} = {{- a} \cdot \left\lbrack {\left( {t - \frac{t_{0}}{2}} \right)^{2} - \frac{t_{0}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Formula 3 when (3t₀/4)≤t≤(t₀)

v(t)=a·(t−t ₀)²  [Formula 3]

wherein t₀ represents a time for conveying the container and arepresents a constant.

In this case, the constant a may be determined as α_(max)/2 whereinα_(max) represents a maximum value of a rate of change of accelerationof the container at which liquid surface oscillations after conveyingthe container can be suppressed within a tolerable range.

Also, when L represents a conveyance distance and V_(max) represents avelocity limit of the container that is tolerable in the conveyance ofthe container, in a case in which a maximum value of the conveyancevelocity v(t) among Formula 1 to 3 is equal to or less than the velocitylimit V_(max), the conveyance time v(t) of the container may be set byusing Formulae 1 to 3; and in a case in which the maximum value of theconveyance velocity v(t) among Formula 1 to 3 is more than the velocitylimit V_(max), a total time for conveying the container in accelerationand in deceleration may be t₁, a time for conveying the container at aconstant speed may be t₂, and the constant may be b, and, in addition,the conveyance velocity v(t) of the container, which is a function oftime t, may be represented by:

Formula 4 when 0≤t≤(t₁/4)

v(t)=b·t ²  [Formula 4]

Formula 5 when (t₁/4)≤t≤(t₁/2)

$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Formula 6 when (t₁/2)≤t≤(t₁/2)+t₂

v(t)=⅛b·t ₁ ²  [Formula 6]

Formula 7 when (t₁/2)+t₂≤t≤(3t₁/4)+t₂

$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2} - t_{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Formula 8 when (3t₁/4)+t₂≤t≤t₁+t₂

v(t)=b·(t−t ₁ −t ₂)²  [Formula 8]

wherein the conveyance velocity v(t) may be set from the conveyance timet₁ and the conveyance time t₂ that are calculated from the constant a,the velocity limit V_(max), and the conveyance distance L where theconstant b is the constant a and the constant speed of Formula 6 is thevelocity limit V_(max).

Also, the first invention may be a method for conveying a containerincluding steps of starting a conveyance by accelerating the containercontaining a liquid in a horizontal direction, conveying the containerat a constant speed, and decelerating the container to complete theconveyance. The conveyance velocity v(t) of the container, which is afunction of time t, can be represented by:

Formula 4 when 0≤t≤(t₁/4)

v(t)=b·t ²  [Formula 4]

Formula 5 when (t₁/4)≤t≤(t₁/2)

$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Formula 6 when (t₁/2)≤t≤(t₁/2)+t₂

v(t)=⅛b·t ₁ ²  [Formula 6]

Formula 7 when (t₁/2)+t₂≤t≤(3t₁/4)+t₂

$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2} - t_{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Formula 8 when (3t₁/4)+t₂≤t≤t₁+t₂

v(t)=b·(t−t ₁ −t ₂)²  [Formula 8]

wherein ‘t₁’ represents a total time for conveying the container inacceleration and in deceleration, ‘t₂’ represents a time for conveyingthe container at a constant speed, and ‘b’ represents a constant.

Also, the first invention may be a method for conveying a container, inwhich the liquid is a molten metal and the container is a tilting ladle.

A second invention is a conveyor control unit for conveying a containerthat starts conveying by accelerating the container containing a liquidin a horizontal direction and completes the conveyance afterdeceleration. The conveyor control unit includes a storage unit and acontrol unit. The storage unit can store a conveyance time t₀ of thecontainer, a constant a, a maximum value of a rate of change ofacceleration α_(max) at which liquid surface oscillations afterconveying the container can be suppressed within a tolerable range. Thestorage unit can also store a conveyance velocity of the container v(t),which is a function of time t, as:

Formula 1 when 0≤t≤(t₀/4)

v(t)=a·t ²  [Formula 1]

Formula 2 when (t₀/4)≤t≤(3t₀/4)

$\begin{matrix}{{v(t)} = {{- a} \cdot \left\lbrack {\left( {t - \frac{t_{0}}{2}} \right)^{2} - \frac{t_{0}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Formula 3 when (3t₀/4)≤t≤(t₀)

v(t)=a·(t−t ₀)²  [Formula 3]

The control unit calculates the constant a from the rate of change ofacceleration αmax stored in the storage unit and can determine theconveyance velocity v(t) of the container.

Here, the storage unit can store a velocity limit V_(max) for thecontainer, which is a tolerable velocity in conveying the container, atotal time t₁ for the container to be conveyed in acceleration anddeceleration, a constant speed time t₂, and a constant b.

The storage unit can also store a conveyance velocity of the containerv(t), which is a function of time t, as:

Formula 4 when 0≤t≤(t₁/4)

v(t)=b·t ²  [Formula 4]

Formula 5 when (t₁/4)≤t≤(t₁/2)

$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Formula 6 when (t₁/2)≤t≤(t₁/2)+t₂

v(t)=⅛b·t ₁ ²  [Formula 6]

Formula 7 when (t₁/2)+t₂≤t≤(3t₁/4)+t₂

$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2} - t_{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Formula 8 when (3t₁/4)+t₂≤t≤t₁+t₂

v(t)=b·(t−t ₁ −t ₂)²  [Formula 8]

When a maximum value of the conveyance velocity v(t) among Formulae 1 to3 is equal to or less than the velocity limit V_(max), the control unitmay be able to set the conveyance time v(t) of the container by usingFormulae 1 to 3; and when the maximum value of the conveyance velocityv(t) among Formulae 1 to 3 is more than the velocity limit V_(max), thecontrol unit can set the conveyance time v(t) of the container by usingFormulae 4 to 8, and, in addition, the control unit may be able tocalculate the conveyance time t₁ and the conveyance time t₂ from theconstant a, the velocity limit V_(max), and the conveyance distance Lwhere the constant b is equal to the constant a and the constant speedof Formula 6 is the velocity limit V_(max).

Effects of the Invention

The present invention can provide a method for conveying a container, ora method for conveying a ladle, which facilitates calculation of aconveyance velocity at which liquid surface oscillations can besuppressed in conveying the container containing a liquid, or the ladlecontaining molten metal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic side view of a casting line for illustrating afirst embodiment of the present invention.

FIG. 2 is a schematic top view of the casting line for illustrating thefirst embodiment of the present invention.

FIG. 3 is a view for illustrating a conveyance velocity of a ladle inthe first embodiment of the present invention.

FIG. 4 is a view for illustrating a relationship between the conveyancevelocity and an acceleration of the ladle in the first embodiment of thepresent invention.

FIG. 5 is a view for illustrating a conveyance distance of the ladle inthe first embodiment of the present invention.

FIG. 6 is a schematic top view of a casting line for illustrating asecond embodiment of the present invention.

FIG. 7 is a view for illustrating a conveyance velocity of a ladle inthe second embodiment of the present invention.

FIG. 8 is a block diagram of a conveyor control device 20.

FIG. 9 is a flowchart showing a control process of the conveyor controldevice 20.

FIG. 10a shows velocity versus time curves V1 and V2.

FIG. 10b shows a velocity versus time curve V3.

DESCRIPTION OF SOME EMBODIMENTS

Hereinafter, some embodiments of the present invention will be describedwith reference to the accompanying drawings. In the embodiments below, amethod for conveying a liquid being contained in a container will bedescribed by illustrating a conveyance of a ladle in a casting line.

First Embodiment

As shown in FIG. 1, a casting line 1 includes a pouring apparatus 2 anda mold conveyor apparatus 3. The pouring apparatus 2 includes a ladle 4containing a molten metal M, a fixing base 5 that supports the ladle 4,and a tilting mechanism 6 that supports the fixing base 5 and tilts theladle 4 together with the fixing base 5. The tilting mechanism 6 issupported by a trolley 7, and a motor 8 drives wheels 9 to rotate sothat the ladle 4 can be conveyed along rails 10 extending in an Xdirection in the drawing. Also, the tilting mechanism 6 and the motor 8are electrically connected to a drive controller unit 11 so that thedrive controller unit 11 can control the position and tilting of theladle 4 in regard to the mold conveyor apparatus 3.

Also, the mold conveyor apparatus 3 includes a conveyor 13, which allowsa mold 12 to move in the X direction in the drawing, and a conveyormotor 14, which drives the conveyor 13 so as to allow the mold 12 to beconveyed. The conveyor motor 14 is electrically connected to a conveyorcontrol unit 15, which can control conveyance of the mold 12.

Next, a procedure for conveying the ladle 4 will be described withreference to FIG. 2.

First, the conveyor control unit 15 of the mold conveyor apparatus 3drives the conveyor motor 14 to convey a plurality of the molds 12placed on the conveyor 13 to predetermined positions (positions A and Bin FIG. 2). Next, the drive controller unit 11 of the pouring apparatus2 drives the motor 8 to rotate the wheels 9 and convey the pouringapparatus 2 along the rails 10 until the ladle 4 is positioned oppositeto a gate G of the mold 12 (the position A in FIG. 2). Then, the drivecontroller unit 11 operates the tilting mechanism 6 to tilt the ladle 4and feeds the molten metal M into the gate G of the mold 12. Whenpouring is finished, the drive controller unit 11 operates the tiltingmechanism 6 once again to tilt the ladle 4 backwards.

After that, the drive controller unit 11 of the pouring apparatus 2drives the motor 8 again to rotate the wheels 9 and convey the pouringapparatus 2 along the rails 10 until the ladle 4 is positioned oppositeto the gate G of the next mold 12 (the position B in FIG. 2). Then, themolten metal is supplied into the gate G of the mold 12 through the sameprocess as at the position A.

The acceleration and deceleration curves of the conveyance velocityversus time curve for the ladle 4 are set to be in S shapes according toformulae below so that liquid surface oscillations after conveying theladle 4 from the position A to the position B can be suppressed.

That is, a conveyance velocity v(t) of the ladle 4 (the velocity in theX direction in the drawing), which is a function of time t, can beobtained, as shown in FIG. 3, by:

Formula 1 when 0≤t≤(t₀/4)

v(t)=a·t ²  [Formula 1]

Formula 2 when (t₀/4)≤t≤(3t₀/4)

$\begin{matrix}{{v(t)} = {{- a} \cdot \left\lbrack {\left( {t - \frac{t_{0}}{2}} \right)^{2} - \frac{t_{0}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$

Formula 3 when (3t₀/4)≤t≤(t₀)

v(t)=a·(t−t ₀)²  [Formula 3]

wherein t₀ represents a time for conveying the ladle 4 and a representsa constant.

In other words, in a graph of conveyance velocity versus conveyancetime, an upwardly convex parabola and a downwardly convex parabolahaving vertical symmetry are prepared in advance, the downwardly convexparabola and the upwardly convex parabola are smoothly connected to forman acceleration curve, the upwardly convex parabola and the downwardlyconvex parabola are smoothly connected to form a deceleration curve, andthe conveyance velocity v(t) shown by the above formulae is obtainedfrom the acceleration curve and the deceleration curve smoothlyconnected where the slope thereof is zero.

The conveyance velocity v(t) of the ladle 4 according to the presentembodiment is obtained by smoothly connecting the downwardly convexparabola represented by Formula 1 (FIG. 3 (1)) and the upwardly convexparabola represented by Formula 2 (FIG. 3 (2)) at a connection pointt=t₀/4 with a slope 2at₀ and by smoothly connecting the upwardly convexparabola represented by Formula 2 and the downwardly convex parabolarepresented by Formula 3 (FIG. 3 (3)) at a connection point t=3t/4 witha slope −2at₀. Accordingly, the curves in an acceleration section(0≤t≤t₀/2) and a deceleration section (t₀/2≤t≤t₀) can be easily set tosmooth S shapes, and thus the liquid surface oscillations of the moltenmetal after conveying the ladle 4 can be suppressed.

Also, as shown in FIG. 4, in the above conveyance velocity v(t), changein time of the curve, i.e. an acceleration dv(t)/dt of the ladle 4, islinear with a slope 2a or −2a. This allows force tilting the liquidsurface during the conveyance to change linearly, and thus liquidsurface oscillations after conveying the ladle 4 can be furthersuppressed.

As a function for an S-shaped curve, a sigmoid function is known. Thisfunction has a curve both ends of which approach its asymptotesgradually, and thus the slope of the curve never becomes zero. Thus, ifthis curve is adapted for the S-shaped curve of the acceleration curveor the deceleration curve, it is required to decide where to set theboth ends of the S shape, i.e. which positions approaching theasymptotes to be set for the both ends. Thus, the S shape may changeaccording to the setting positions for the both ends, which increasesparameters to determine the S shape, and, as a result, setting of theacceleration or deceleration curves becomes complicated.

On the other hand, the S-shaped curve according to the presentembodiment is a curve connecting symmetric parabolas, and thus the bothends may be set at positions where the slope of the curve is zero. Andsetting the positions for the both ends can uniquely determine the shapeof the parabolas, accordingly determining the shape of the S-shapedcurve uniquely. This can set the S shape of the acceleration curve andthe deceleration curve easily and thus set the conveyance velocityeasily.

Although parabolas (a quadratic function) are used in the presentembodiment, a higher function such as a cubic or quartic function may beused as necessary. The higher the function is, the more smooth S-shapedcurves can be. However, using the quadratic function for the velocitychange allows a rate of change of acceleration to be a linear function.This facilitates velocity setting using a tolerable maximum rate ofchange of acceleration, which will be described below.

As shown in FIG. 5, a conveyance distance L of the ladle 4 can berepresented as an integrated value of v(t) in 0≤t≤(t₀/2) i.e. at₀ ³/16.Thus, the constant a is 16 L/t₀ ³, which can be determined from theconveyance distance L and the conveyance time t₀. Accordingly, theconveyance velocity v(t) can be easily set by the conveyance time t₀ andthe conveyance distance L.

As above, according to the present embodiment, the conveyance velocityv(t) of the ladle 4 can be easily set by using parabolas in whichacceleration and deceleration curves are in S shapes, and, inparticular, the conveyance time to and the conveyance distance L caneasily determine the conveyance velocity v(t). Thus, it is possible toset the conveyance velocity v(t) with less parameters and simplerformulae than in a liquid simulation.

For example, when the conveyance distance L is predetermined, theconveyance velocity v(t) according to the present embodiment can bedetermined by performing a conveyance experiment based on the formulaefor the conveyance velocity v(t). In the experiment, the conveyance timeto is gradually decreased, and the conveyance velocity v(t) isdetermined by setting the conveyance time to within a range in whichliquid surface oscillations after the conveyance are tolerable.

On the other hand, when the conveyance time to is predetermined, todetermine the conveyance velocity v(t), the conveyance distance L isdecreased gradually in the conveyance experiment performed based on theformulae for the conveyance velocity v(t). The conveyance velocity v(t)is then determined by setting the conveyance distance L within a rang inwhich liquid surface oscillations after the conveyance are tolerable.

The formulae for the conveyance velocity v(t) are stored in the drivecontroller unit 11 in the casting line 1 so that the drive controllerunit 11 drives and controls the motor 8 to convey the ladle 4 inaccordance with the v(t). At that time, it is preferable that the drivecontroller unit 11 is connected to an input device, for example, so thatthe conveyance time to and the conveyance distance L can be changed fromoutside.

Alternatively, the velocity versus time curves of Formula 1 to Formula 3may be determined by using a maximum value of the rate of change ofacceleration α_(max) of the container at which the liquid surfaceoscillations after conveying the ladle 4 can be suppressed within thetolerable range. The rate of change of acceleration α_(max) can becalculated by time-differentiating the acceleration. That is, by makingthe rate of change of acceleration of the velocity versus time curve ofFormula 1 equal to the maximum value α_(max), the ladle 4 can beconveyed at the maximum conveyance velocity (i.e. within the minimumconveyance time) while suppressing the liquid surface oscillations afterconveying the ladle 4 within the tolerable range.

In Formula 1, the maximum value for the rate of change of accelerationis 2a, and thus the maximum value for the constant a can be calculatedas α_(max)/2 (hereinafter, represented as a_(max)). Also, at that time,from the relational expression shown in FIG. 5, the conveyance time t₀for the ladle 4 to be conveyed for the conveyance distance L can becalculated as (16L/a_(max))^(1/3) (hereinafter, represented ast_(0-min)).

Using the calculated a_(max) and t_(0-min) to set the coefficients ofFormula 1 to Formula 3 can set the velocity versus time curve in whichthe ladle 4 can be conveyed for the conveying distance L within aminimum time while suppressing liquid surface oscillations afterconveying the ladle 4 within the tolerable range.

Also, from the relational expression shown in FIG. 5, the conveyancedistance L for the ladle 4 to be conveyed within the conveyance time t₀can be calculated as a_(max)·t₀ ³/16.

The rate of change of acceleration α_(max) may be predetermined from acalculation or an experiment in accordance with, for example, a shapeand content of the container, an amount of content, the rigidity of theapparatus, and so on.

Second Embodiment

A method for conveying a liquid being contained in a container will bedescribed, similarly to the first embodiment, by illustrating aconveyance of a ladle. The same notations will be used to illustrate thesame device and structures as in the first embodiment.

As shown in FIG. 2, the first embodiment is described by illustrating aconveyance of the ladle 4 from the position A to B, which is aconveyance for a relatively short distance. However, in a case in whichthe ladle 4 is conveyed for a relatively long distance, such as from theposition A to C as shown in FIG. 6, the conveyance velocity v(t)calculated by using the formulae according to the first embodiment maytend to become large, and, in order to suppress the liquid surfaceoscillations after the conveyance, it may become difficult to reduce theconveyance time t₀. In such a case, it is preferable that the formulaefor the conveyance velocity v(t) according to the first embodiment arereviewed and determined as follows.

That is, the ladle 4 is accelerated in a horizontal direction, conveyedat a constant speed, and then decelerated. The conveyance velocity v(t)of the ladle 4 (the velocity in the X direction in the drawing), whichis a function of time t, can be obtained, as shown in FIG. 7, by:

Formula 4 when 0≤t≤(t₁/4)

v(t)=b·t ²  [Formula 4]

Formula 5 when (t₁/4)≤t≤(t₁/2)

$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Formula 6 when (t₁/2)≤t≤(t₁/2)+t₂

v(t)=⅛b·t ₁ ²  [Formula 6]

Formula 7 when (t₁/2)+t₂≤t≤(3t₁/4)+t₂

$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2} - t_{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Formula 8 when (3t₁/4)+t₂≤t≤t₁+t₂

v(t)=b·(t−t ₁ −t ₂)²  [Formula 8]

wherein t₁ represents a total time for conveying the ladle 4 inacceleration and in deceleration, t2 represents a time for conveying theladle 4 at a constant speed (i.e. t₁+t₂ is the conveyance time), Lrepresents the conveyance distance, and b represents a constant.

In other words, in a graph of conveyance velocity versus conveyancetime, an upwardly convex parabola and a downwardly convex parabolahaving vertical symmetry are prepared in advance, the downwardly convexparabola and the upwardly convex parabola are smoothly connected to forman acceleration curve, the upwardly convex parabola and the downwardlyconvex parabola are smoothly connected to form a deceleration curve, andthe conveyance velocity v(t) shown by the above formulae is obtainedfrom smoothly connecting the acceleration curve with the decelerationcurve via a horizontal straight line.

The conveyance velocity v(t) of the ladle 4 according to the presentembodiment is obtained by smoothly connecting the downwardly convexparabola represented by Formula 4 and the upwardly convex parabolarepresented by Formula 5 at a connection point t=t₀/4 with a slope 2at₀(FIG. 7, section 1) and by smoothly connecting the upwardly convexparabola represented by Formula 7 and the downwardly convex parabolarepresented by Formula 8 at a connection point t=3t₁/4+t₂ with a slope−2at₀ (FIG. 7, section 3). Accordingly, the curves in an accelerationsection (0≤t≤t₀/2) and the deceleration section (t₁/2+t_(2≤)t≤t₁+t₂) canbe easily set to smooth S shapes so that liquid surface oscillations ofthe molten metal after conveying the ladle 4 can be suppressed.

Also, the conveyance velocity v(t) includes a constant speed section[(t₁/2)≤t≤(t₁/2)+t₂] (FIG. 7, section 2), which smoothly connects withthe upwardly convex parabolas, between the acceleration section and thedeceleration section. This can suppress the conveyance velocity v(t)from increasing excessively and also suppress the liquid surfaceoscillations of the molten metal after a short conveyance time (t₁+t₂)of conveying the ladle 4.

As shown in FIG. 7, the conveyance distance L of the ladle 4 can berepresented as an integrated value of v(t) in 0≤t≤(t₁+t₂) i.e. b(t₁³+2t₁ ²t2)/16. Thus, the constant b is 16 L/(t₁ ³+2t₁ ²t₂), which can bedetermined from the total time t₁ of acceleration and deceleration, theconstant speed time t₂, and the conveyance distance L of the ladle 4.Accordingly, the conveyance velocity v(t) of the ladle 4 can be easilyset by the total time t₁ of acceleration and deceleration, the constantspeed time t₂, and the conveyance distance L.

As above, according to the present embodiment, also in a case in whichthe conveying distance L is relatively long, the conveyance velocityv(t) of the ladle 4 at which liquid oscillations can be suppressedwithin a tolerable range can be easily set, and in particular, the totaltime t₁ of acceleration and deceleration, the constant speed time t₂,and the conveyance distance L can easily determine the conveyancevelocity v(t).

For example, when the conveyance distance L is predetermined, theconveyance velocity v(t) can be determined by performing a conveyanceexperiment based on the formulae for the conveyance velocity v(t). Inthe experiment, the total time of acceleration and deceleration t₁ andthe conveyance time at the constant speed t₂ are gradually decreased,and the conveyance velocity v(t) is determined by setting the total timeof acceleration and deceleration t₁ and the constant speed conveyancetime t₂ within a range in which liquid surface oscillations after theconveyance are tolerable.

On the other hand, when the conveyance time to is predetermined, todetermine the conveyance velocity v(t), the conveyance distance L isdecreased gradually in the conveyance experiment performed based on theformulae for the conveyance velocity v(t). The conveyance velocity v(t)is then determined by setting the conveyance distance L within a rangein which liquid surface oscillations after the conveyance are tolerable.

Next, a conveyor control device that can achieve the method forconveying the ladle 4 described in the above embodiments will beexemplified.

As shown in FIG. 8, a conveyor control device 20 can be configured by acomputer, for example, and can be connected with a storage unit 21 suchas RAM or a hard disk drive. The storage unit 21 can store theabove-mentioned Formulae 1 to 8 and can also store the maximum value ofthe rate of change of acceleration □_(max) at which liquid surfaceoscillations after conveying the ladle 4 can be suppressed within atolerable range, a velocity limit V_(max), which is a tolerable velocitythat the conveyor device is capable of in conveying the ladle 4, and thelike. Also, a conveyor control unit 15 can input information needed forthe control into the storage unit 21 and, in reverse, can output variousinformation needed for the control from the storage unit 21.

The conveyor control unit 15 can also perform various operations andcontrol of various parts by means of a CPU or the like. Also,information necessary for the control can be stored in the storage unit21 by using an input unit 22 such as a keyboard and, also, content ofthe control can be shown on an output unit 23 such as a display.

FIG. 9 is a flowchart showing a control process using the conveyorcontrol device 20. In the control using the conveyor control device 20,the conveyor control unit 15 firstly sets the conveyance distance L ofthe ladle 4 (Step 100). Here, an operator may input the conveyancedistance L through the input unit 22, or the conveyance distance L maybe stored in the storage unit 21 in advance and the conveyor controlunit 15 may read the conveyance distance L from the storage unit 21.

Next, the conveyor control unit 15 sets a velocity versus time curve V1as shown in FIG. 10a as the conveyance velocity v(t) of the ladle 4using Formulae 1 to 3 (Step 101). Then, the conveyor control unit 15reads the maximum value of the rate of change of acceleration α_(max),which has been stored in the storage unit 21, and calculates a_(max),which is the constant a when the maximum rate of change of accelerationof the velocity versus time curve V1 (the time integration of Formula 1in actuality) is α_(max), to find the shortest conveyance time t_(0-min)by calculating the conveyance time t₀ for the ladle 4 to be conveyed forthe conveyance distance L (Step 102). Then, coefficients of Formulae 1to 3 are determined from the calculated constant a_(max) and theconveyance time t_(0-min) (Step 103).

Next, the conveyor control unit 15 reads the velocity limit V_(max),which has been stored in the storage unit 21, and the velocity limitV_(max) is compared with the maximum value of the velocity versus timecurve V1 (the maximum value of Formula 2 in actuality), of which thecoefficients have been calculated in Step 103 (Step 104). Here, if theconveyance velocity v(t) of the ladle 4, i.e. the maximum value of thevelocity versus time curve V1, is equal to or less than the velocitylimit V_(max) (Step 104), the velocity versus time curve V1 usingFormulae 1 to 3 is decided as the final velocity versus time curve forthe ladle 4 and the conveyance velocity v(t) in accordance with thiscurve is determined as the conveyance velocity for the ladle 4 (Step109). The velocity versus time curve V1 at this time, i.e. theconveyance velocity v(t), may be stored in the storage unit 21 so as tobe read out as necessary.

On the other hand, if the conveyance velocity v(t) of the ladle 4, i.e.the maximum value of the velocity versus time curve V1, is larger thanthe velocity limit V_(max), the conveyor control unit 15 cancels thesetting of the conveyance velocity v(t) of the ladle 4, i.e. thevelocity versus time curve V1, and, by using Formulae 4 to 8, sets a newvelocity versus time curve including the accelerating section—constantspeed section—deceleration section as the conveyance velocity v(t) forthe ladle 4 (Step 105). That is, to a velocity versus time curve such asV1 in which an acceleration section and a deceleration section arecontinuous, a constant speed section is newly added between theacceleration section and the deceleration section to form a new velocityversus time curve. FIG. 10b shows a velocity versus time curve V3, whichis an example of a velocity versus time curve to be set.

Next, the conveyor control unit 15 calculates the constant b, t1, and t2for Formulae 4 to 8 on a condition that the ladle 4 can be conveyed at aspeed less than the velocity limit V_(max) for the conveyance distance Lin the shortest possible conveyance time.

That is, the constant b is set as a_(max), which has been calculated inStep 102, so that the time t₁, which is the total time for the ladle 4to be conveyed while being accelerated and decelerated, is minimum.Then, the conveyance velocity t₁ is calculated with a constant ofFormula 6 as V_(max) so that the maximum value of the velocity versustime curve set in Step 105 is equal to the velocity limit V_(max) (Step106).

The calculated conveyance time t₁, in regard to the velocity versus timecurve determined in Step 105, is the total conveyance time wherein theconstant b of the formula for the accelerating section and thedecelerating section of the ladle 4 is a_(max), the maximum value of thevelocity versus time curve V3 is V_(max), and the conveyance time duringthe constant speed section t₂ is zero, and is equivalent to the totalconveyance time of a velocity versus time curve V2 in FIG. 10 a.

Next, the conveyance time t₂ is calculated by using the alreadydetermined constant b (=a_(max)) and the already calculated conveyancetime t₁ so that the integrated value of Formulae 4 to 8 from the timezero to the time t₁+t₂ is equal to the conveyance distance L (Step 107).The conveyance time t₂ is calculated so that an area between thevelocity versus time curve V1 and the velocity versus time curve V2 inFIG. 10a (a shaded section A1) is equal to to an area of the constantspeed section of the velocity versus time curve V3 in FIG. 10 b.

Then, the coefficients of Formulae 4 to 8 are determined with the setconstant b (=a_(max)) and the calculated conveyance times t₁ and t₂ todetermine the velocity versus time curve V3 shown in FIG. 10b (Step108).

Lastly, the conveyor control unit 15 determines the velocity versus timecurve V3 using Formulae 4 to 8 as the final velocity versus time curvefor the ladle 4 and the conveyance velocity v(t) in accordance with thiscurve is determined as the conveyance velocity for the ladle 4 (Step109). The velocity versus time curve V3 at this time, i.e. theconveyance velocity v(t), may be stored in the storage unit 21 so as tobe read out as necessary.

Although some embodiments of the present invention have been describedby illustrating a conveyance of a ladle containing molten metal in acasting line, the technical scope of the present invention is notlimited thereto. The present invention can be also applied to, forexample, a line of manufacturing food or chemicals, where it is requiredthat a container containing a liquid material for making such product isconveyed while preventing the liquid from spilling out of the containerand suppressing liquid surface oscillations after the conveyance.

DESCRIPTION OF NOTATIONS

-   1 . . . casting line-   2 . . . pouring apparatus-   3 . . . mold conveyor apparatus-   4 . . . ladle-   5 . . . fixing base-   6 . . . tilting mechanism-   7 . . . trolley-   8 . . . motor-   9 . . . wheel-   10 . . . rail-   11 . . . drive controller unit-   12 . . . mold-   13 . . . conveyor-   14 . . . conveyor motor-   15 . . . conveyor control unit-   20 . . . conveyor device-   21 . . . storage unit-   22 . . . input unit-   23 . . . display unit-   M . . . molten metal-   G . . . gate

1. A method for conveying a container, comprising: starting a conveyanceby accelerating the container containing a liquid in a horizontaldirection; and decelerating the container to complete the conveyance,wherein a conveyance velocity v(t) of the container, which is a functionof time t, is represented by: Formula 1 when 0≤t≤(t₀/4)v(t)=a·t ²  [Formula 1] Formula 2 when (t₀/4)≤t≤(3t₀/4) $\begin{matrix}{{v(t)} = {{- a} \cdot \left\lbrack {\left( {t - \frac{t_{0}}{2}} \right)^{2} - \frac{t_{0}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$ Formula 3 when (3t₀/4)≤t≤(t₀)v(t)=a·(t−t ₀)²  [Formula 3] wherein ‘t₀’ represents a time forconveying the container and ‘a’ represents a constant.
 2. A method forconveying a container, comprising: starting a conveyance by acceleratingthe container containing a liquid in a horizontal direction; conveyingthe container at a constant speed; and decelerating the container tocomplete the conveyance, wherein a conveyance velocity v(t) of thecontainer, which is a function of time t, is represented by: Formula 4when 0≤t≤(t₁/4)v(t)=b·t ²  [Formula 4] Formula 5 when (t₁/4)≤t≤(t₁/2) $\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$ Formula 6 when (t₁/2)≤t≤(t₁/2)+t₂v(t)=⅛b·t ₁ ²  [Formula 6] Formula 7 when (t₁/2)+t₂≤t≤(3t₁/4)+t₂$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2} - t_{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$ Formula 8 when (3t₁/4)+t₂≤t≤t₁+t₂v(t)=b·(t−t ₁ −t ₂)²  [Formula 8] wherein ‘t₁’ represents a total timefor conveying the container in acceleration and in deceleration, ‘t₂’represents a time for conveying the container at a constant speed, and‘b’ represents a constant.
 3. The method for conveying a containeraccording to claim 1, wherein the constant a is determined as α_(max)/2wherein α_(max) represents a maximum value of a rate of change ofacceleration of the container at which liquid surface oscillations afterconveying the container is suppressed within a tolerable range.
 4. Themethod for conveying a container according to claim 3, wherein aconveyance distance of the container is L and a velocity limit of thecontainer that is tolerable in conveying the container is V_(max); theconveyance velocity v(t) of the container is set by Formulae 1 to 3 whena maximum value of the conveyance velocity v(t) among Formula 1 to 3 isequal to or less than the velocity limit V_(max); and when the maximumvalue of the conveyance velocity v(t) among Formulae 1 to 3 is more thanthe velocity limit V_(max), a total time for conveying the container inacceleration and in deceleration is t₁, a time for conveying thecontainer at a constant speed is t₂, and the constant is b, and, inaddition, the conveyance velocity v(t) of the container, which is afunction of time t, is represented by: Formula 4 when 0≤t≤(t₁/4)v(t)=b·t ²  [Formula 4] Formula 5 when (t₁/4)≤t≤(t₁/2) $\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$ Formula 6 when (t₁/2)≤t≤(t₁/2)+t₂v(t)=⅛b·t ₁ ²  [Formula 6] Formula 7 when (t₁/2)+t₂≤t≤(3t₁/4)+t₂$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2} - t_{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$ Formula 8 when (3t₁/4)+t₂≤t≤t₁+t₂v(t)=b·(t−t ₁ −t ₂)²  [Formula 8] wherein the conveyance velocity v(t)is set from the conveyance time t₁ and the conveyance time t₂ that arecalculated from the constant a, the velocity limit V_(max), and theconveyance distance L where the constant b is the constant a and theconstant speed of Formula 6 is the velocity limit V_(max).
 5. The methodfor conveying a container according to claim 1, wherein the liquid is amolten metal and the container is a tilting ladle.
 6. A conveyor controlunit for conveying a container, which starts conveying by accelerating acontainer containing a liquid in a horizontal direction and completesthe conveyance after deceleration, the conveyor control unit comprising:a storage unit; and a control unit, wherein the storage unit stores aconveyance time t₀ of the container, a constant a, a maximum value of arate of change of acceleration of the container α_(max) at which liquidsurface oscillations after conveying the container is suppressed withina tolerable range; the storage unit also stores a conveyance velocity ofthe container v(t), which is a function of time t as: Formula 1 when0≤t≤(t₀/4)v(t)=a·t ²  [Formula 1] Formula 2 when (t₀/4)≤t≤(3t₀/4) $\begin{matrix}{{v(t)} = {{- a} \cdot \left\lbrack {\left( {t - \frac{t_{0}}{2}} \right)^{2} - \frac{t_{0}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\end{matrix}$ Formula 3 when (3t₀/4)≤t≤(t₀)v(t)=a·(t−t ₀)  [Formula 3] ; and the control unit calculates theconstant a from the rate of change of acceleration α_(max) stored in thestorage unit and determines the conveyance velocity v(t) of thecontainer.
 7. The conveyor control unit for conveying a containeraccording to claim 6, wherein the storage unit stores a velocity limitV_(max) for the container, which is tolerable in conveying thecontainer, a total time t₁ for the container to be conveyed inacceleration and deceleration, a constant speed time t₂, and a constantb; the storage unit also stores a conveyance velocity of the containerv(t), which is a function of time t as: Formula 4 when 0≤t≤(t₁/4)v(t)=b·t ²  [Formula 4] Formula 5 when (t₁/4)≤t≤(t₁/2) $\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 5} \right\rbrack\end{matrix}$ Formula 6 when (t₁/2)≤t≤(t₁/2)+t₂v(t)=⅛b·t ₁ ²  [Formula 6] Formula 7 when (t₁/2)+t₂≤t≤(3t₁/4)+t₂$\begin{matrix}{{v(t)} = {{- b} \cdot \left\lbrack {\left( {t - \frac{t_{1}}{2} - t_{2}} \right)^{2} - \frac{t_{1}^{2}}{8}} \right\rbrack}} & \left\lbrack {{Formula}\mspace{14mu} 7} \right\rbrack\end{matrix}$ Formula 8 when (3t₁/4)+t₂≤t≤t₁+t₂v(t)=b·(t−t ₁ −t ₂)²  [Formula 8] ; and when a maximum value of theconveyance velocity v(t) among Formulae 1 to 3 is equal to or less thanthe velocity limit V_(max), the control unit sets the conveyance timev(t) of the container by using Formulae 1 to 3; and when the maximumvalue of the conveyance velocity v(t) among Formulae 1 to 3 is more thanthe velocity limit V_(max), the control unit sets the conveyance timev(t) of the container by using Formulae 4 to 8, and, in addition, thecontrol unit calculates the conveyance time t₁ and the conveyance timet₂ from the constant a, the velocity limit V_(max), and the conveyancedistance L where the constant b is equal to the constant a and theconstant speed of Formula 6 is the velocity limit V_(max).
 8. The methodfor conveying a container according to claim 2, wherein the liquid is amolten metal and the container is a tilting ladle.